So... of course you are logged into Google Wave all of the time, looking for new blips in your wavelets constantly.
When, by chance, you have logged out, navigated away from Wave, or whatever, it would be nice to be notified when updates have occurred, wouldn't it?
Now there is the Google Wave Add-on for Firefox. It shows you the number of unread messages, and whenever new messages arrive it pops up a small notification window.
Go check it out at
http://thatsmith.com/2009/10/google-wave-add-on-for-firefox or install it directly by clicking here